Dyno Run Result for my Z4M Roadster....

[billy_beemer]

Ahoy!

So a chap from my office mentioned to me in the middle of last week that he was getting his car dyno'd at Eurospec 2000 in Guildford with his beloved FTO Car Club.....

Having just been brave and swapped out the OEM exhaust for a very nice Supersprint X-Pipe and set of the bigger 80mm racing mufflers sold to me by a very nice chap on Pistonheads I thought it would be good to see the results.

So I went along and after pointing out to all the other participants that their engines were small, mounted the wrong way and driving the wrong set of wheels we began lol.

Here is the main result page (1/3)

Max Power 319.3 HP
At the wheel 264.3 HP

The torque line looks very flat and I'm also very pleased with how smooth the power delivery curve is. The max torque figure looks to be around 255 lb-ft which translates to 345nm

In all cases I appear to be a good smidge below the OEM figures which are 338 (or 342 depending on where you look) BHP and 365 Nm 269 lb-ft

Since fitting the supersprint the car is much much MUCH smoother, even in Sport mode the jerky motion you can get from the throttle has really smoothed out.

Conditions wise, it was a warm day on Sunday (18 degrees) and the car usually runs on Tesco 99 and today was no exception.

So the reason for the post?
- Well dyno results are always interesting (particularly when they're your own)
- Has my tinkering with the exhaust made the car less powerful, I suspect not, I think it's smoothed out the torque line but then there's a lot of talk of the effects of back pressure with the OEM system
- Should I try and 'restore' that extra 20 horse power? Is it worth a tune
- Am I probably right in thinking it never had that extra 20 horse power lol

I know there's posts out there claiming you can get 380bhp but really I'm hoping there might be some mileage in getting a rolling re-map and maybe squeezing it back in the 340-350 direction.
I'm also willing to be convinced that 320 is about right and that I should spend the money on more super unleaded instead lol.....

Discuss

 

[daz05]

I've heard of a few of these dyno around that number but i've also heard of others going to around 330. I think BMW quote bhp before the cats hence why most go below.

I remember driving mine back to back with a friends and mine felt quicker so you do get good ones and bad ones.

 

[mmm-five]

I call bollocks on the dyno myself, as I don't believe your car revved to 8400rpm - mine hits the limiter at 8000rpm - so if that's wrong, what else is wrong?

The only figure that I'd take away from a dyno would be the wheel HP as everything else is a guesstimate - although the measured RWHP can be manipulated/incorrect depending on tyre pressures, condition of rollers, strapping, etc.

 

[billy_beemer]

I'm not convinced by the 8,400rpm figure either. The test was run in 4th gear if that makes any odds to the limiter. At the wheel power came out at 264.3 BHP, still seems low to me.......

 

[daz05]

It's making power too early and max torque too late also. Strange.

Should be making max power at 7900 rpm and max torque at 4900rpm

 

[original guvnor]

This was my dyno graph, done 12 months ago. The guy only revved it to just under 7,400 though because he reckoned his machine was near its limits. You can see my torque curve looks almost spot on the factory claimed figures.

 

[ga41]

319hp engine and 264hp at the wheels? That works out at 21% drivetrain loss. Way too much drivetrain loss...

Also don't be dismayed that you didn't post the stock numbers, if the dyno operator wanted to he could've made it show that you had 400 (see drivetrain loss above for example) plus the S54 is known to not post the factory numbers in the first place...

 

[billy_beemer]

This was my dyno graph, done 12 months ago. The guy only revved it to just under 7,400 though because he reckoned his machine was near its limits. You can see my torque curve looks almost spot on the factory claimed figures.

I don't think the RPM plot is accurate. I don't think it goes to 8,400rpm without the limiter kicking in? 7,500 sounds far more like it to me.....

 

[billy_beemer]

319hp engine and 264hp at the wheels? That works out at 21% drivetrain loss. Way too much drivetrain loss...

Also don't be dismayed that you didn't post the stock numbers, if the dyno operator wanted to he could've made it show that you had 400 (see drivetrain loss above for example) plus the S54 is known to not post the factory numbers in the first place...

17.2% is that really that bad? Not sure how you worked that out as 21% lol

319 * 0.172 = 55bhp (the loss)

The car has covered 10k since its last service which, blimey was February last year now. It's booked in for next week.

Also when it had its inspection II carried out my specialist recommended we delay tappet alignment, he checked them and said they were all within tolerance and should check them again when we do the next OIL service.

Could the tappets and the need some new oil make up the difference?

I am more than willing to spend some money getting the car rolling road tuned if its worth it. But I'm not convinced it will make a big difference?

 

[ga41]

17.2% is that really that bad? Not sure how you worked that out as 21% lol

319 * 0.172 = 55bhp (the loss)

17.2% of 264 is 45.408 not 55

Shouldn't we calculate the loss using the wheel horsepower? After all it's the only piece of hard data that we have, what the dyno spits out before any correcting factors are added to to calculate the power at the flywheel. :?

Correct me if i'm wrong, but in either case you shouldn't put much stock in it, some dynos are more conservative than others and losses aren't REALLY a fixed percentage anyway. Dynos should only be used for before/after comparisons in my opinion...

edit: Also i'm pretty tired so if i'm talking out of my ass please forgive me.

 

[billy_beemer]

eh? 17.2% of 319HP = the at the wheel power of 264.3HP...................

you wouldn't deduct a percentage from the at the wheel figure.

 

[Adelphi2]

Ga41 is right. Dynos are only useful for before & after comparisons. Dynos are very subjective bits of kit. No two are the same.

 

[ga41]

eh? 17.2% of 319HP = the at the wheel power of 264.3HP...................

you wouldn't deduct a percentage from the at the wheel figure.

Why would you do it that way? Shouldn't you add the losses from the at the wheels? After all the whp is the data that we start with right?

 

[tertius]

eh? 17.2% of 319HP = the at the wheel power of 264.3HP...................

you wouldn't deduct a percentage from the at the wheel figure.

Why would you do it that way? Shouldn't you add the losses from the at the wheels? After all the whp is the data that we start with right?

Because you are calculating the loss from the flywheel.

Assuming it is done correctly (using coastdown measurements) the dyno flywheel figure is actually more accurate and useful than the wheels figure. As someone said above the wheels result can be easily manipulated, e.g. by changing tyre pressures, but the coastdown measurement will cancel this out, and should therefore, give a reasonably reliable value. The drivetrain "loss" is just a verification really, i.e. "does that seem about right?"

Though again as said, dynos do vary and their real value is in comparing the effect of modifications where you run before and after on the same dyno, with the same operator, on the same day if possible.

 

[ga41]

eh? 17.2% of 319HP = the at the wheel power of 264.3HP...................

you wouldn't deduct a percentage from the at the wheel figure.

Why would you do it that way? Shouldn't you add the losses from the at the wheels? After all the whp is the data that we start with right?

Because you are calculating the loss from the flywheel.

Assuming it is done correctly (using coastdown measurements) the dyno flywheel figure is actually more accurate and useful than the wheels figure. As someone said above the wheels result can be easily manipulated, e.g. by changing tyre pressures, but the coastdown measurement will cancel this out, and should therefore, give a reasonably reliable value. The drivetrain "loss" is just a verification really, i.e. "does that seem about right?"

Though again as said, dynos do vary and their real value is in comparing the effect of modifications where you run before and after on the same dyno, with the same operator, on the same day if possible.

ΟΚ now i realise that the proper way to calculate losses is the other way from what i originally said but then again i can't help thinking that the only piece of unprocessed data is the whp. The flywheel data posted has already been through processing right? It just doesn't feel right!

 

[flimper]

My effort

 

[tertius]

ΟΚ now i realise that the proper way to calculate losses is the other way from what i originally said but then again i can't help thinking that the only piece of unprocessed data is the whp. The flywheel data posted has already been through processing right? It just doesn't feel right!

The whp value is unprocessed, but it is not the only piece of unprocessed data, the other item is the coastdown data. Now to be fair we can't see the coastdown data from what has been posted but it ought to be available.

As previously said the whp value is extremely susceptible to manipulation (intentional or not), however, the coastdown values will be be subject to the same variables, but "inversely"', therefore, when you apply the coastdown values to calculate the flywheel output, you cancel out these variables and get a much more reliable figure.

I have some dyno charts that show the coastdown graphs, will try to post them later when I am on a PC.

 

[billy_beemer]

My effort

I saw this during my googling before posting mine. Wasn't there a general feeling that surrey rolling road is a bit... generous

So which is best, your surrey rolling road 340bhp or my eurospec 319? there's only one way to find out....

RACE !!!!

 

[ga41]

I saw this during my googling before posting mine. Wasn't there a general feeling that surrey rolling road is a bit... generous

So which is best, your surrey rolling road 340bhp or my eurospec 319? there's only one way to find out....

RACE !!!!

Hell yea. If i was in the UK i'd be up for it.

 

[tomscott]

Is it not worth remapping after an exhaust or any mods so the ecu isn't compensating so you get a map that is custom to your mods? I'm no expert just asking?

Also I thought most would be around 330 on a rolling road.